Semiconductor device and method for manufacturing same

ABSTRACT

To provide a semiconductor device that is capable of transmitting heat evolved in an active element efficiently to a heat sink member, and a manufacturing method for the semiconductor device. One of the terminals (such as drain electrode) of an active element formed in a substrate of, for example, GaAs, is thermally contacted with a heat sink member via an insulating member of, for example, aluminum nitride, exhibiting thermally conductive and electrically insulating properties. The heat sink member may, for example, be an electrically conductive member connected to another terminal of the active element, or a heat sink of a package.

FIELD OF THE INVENTION

[0001] This invention relates to a semiconductor device and, moreparticularly, to a high-output-power field-effect transistor (FET)connected to a package by a face-down system.

RELATED ART

[0002] The semiconductor device, formed of a GaAs based semiconductormaterial, is used in a majority of cases as a semiconductor device forwhich high-speed response is required in view of its characteristics asa material. However, since heat evolution in an element deterioratescharacteristics of the semiconductor device, there is presented aproblem of how to improve the cooling efficiency of the device.

[0003] For example, in a semiconductor device of the type of dissipatingthe heat evolved from the semiconductor substrate, there is used atechnique of reducing the thickness of the GaAs substrate having lowthermal conductivity to assist in thermal diffusion (heat dissipation).However, the semiconductor device suffers from a drawback that, if thesubstrate is reduced in thickness, the device is lowered in mechanicalstrength. For increasing the thermal diffusion (heat dissipation)efficiency without weakening the mechanical strength, there is disclosedin, for example, the JP Patent Kokai JP-A-59-124750 and JP Patent KokaiJP-06-005633, a method for interconnecting a substrate and a heat sinkvia an electrically conductive layer.

[0004] On the other hand, in a semiconductor device of the type in whichthe heat evolved from the device is dissipated from an electrode on thesemiconductor substrate surface provided with the insulating film or theelectrode, there is used a technique of dissipating the heat via anelectrically conductive member electrically connected to the electrodeor a heat sink member.

[0005] In particular, in the high-output-power field effect transistor(FET), there is routinely used flip-chip mounting of the face-downsystem in which a gate electrode interconnection formed on a GaAssubstrate is intimately contacted with the package heat sink.

[0006]FIG. 12 shows the cross-section of a conventional semiconductordevice, while FIG. 13 shows the cross-section of the semiconductordevice of FIG. 12 mounted on a package.

[0007] Referring to FIGS. 12 and 13, the manufacturing method of aconventional semiconductor device is explained step-by-step.

[0008] Referring to FIG. 12, a gate electrode 2 is first formed on asubstrate of, for example, GaAs, and subsequently a first insulatingfilm 7 is deposited on the entire surface of the substrate 1. At areasof the first insulating film 7 in which a source electrode 4 and a drainelectrode 3 are formed, holes are formed, and TiAu sputtering is thenapplied to form an electrically conductive layer for plating followed byAu plating to form the source electrode 4 and the drain electrode 3.

[0009] A second insulating film 8 is then deposited on the entiresurface to overlie the first insulating film 7, source electrode 4 andthe drain electrode 3 and planarized. The area of the planarized secondinsulating film 8 in register with the source electrode 4 is then bored,i.e. the exposed portion (bore in a mask) of the second insulating film8 is removed. Then, TiAu etc. designed to serve as an electricallyconductive layer for the plating is sputtered on the entire surface toform a thick plating film of Au resulting in an electrically conductivemember 6. This gives an active element having a cross-sectional shape asshown in FIG. 12.

[0010] The active element, shown in FIG. 12, is bonded by thermalpressure bonding to a package heat sink 9 by the face-down system toeffect flip-chip mounting, as shown in FIG. 13.

SUMMARY OF THE DISCLOSURE

[0011] However, in the course of the investigations toward the presentinvention the following problems have been encountered. Namely, theabove-described conventional semiconductor device has the followingdrawbacks. Referring to FIG. 14, schematically illustrating thedrawbacks of the conventional semiconductor device shown in FIG. 13, thethermal diffusion (heat dissipation) path 13 is solely a path connectingfrom the source electrode 4 via the electrically conductive member 6 tothe package heat sink 9, while there is no heat conducting path for theheat evolved on the side of the drain electrode 3, so that the heatevolved on the semiconductor device cannot be dissipated efficientlytowards the package.

[0012] In view of the above drawbacks, it is an object of the presentinvention to provide a semiconductor device which is capable ofdissipating the heat evolved on the semiconductor device efficientlytowards the package, and a manufacturing method therefor.

[0013] For accomplishing the above object, the present inventionprovides a device in which an insulator having high electricalinsulating properties and high thermal conductivity above (on top of) adrain electrode and in which this insulator is thermally contacted witha lead-out interconnection layer of a source electrode.

[0014] According to the present invention, generally, there is provideda semiconductor device comprising:

[0015] a plurality of heat dissipating paths, each for each of a pre-setnumber of terminals of an active element, the heat dissipating pathsbeing adapted for transmitting heat from the terminals of the activeelement to a heat sink member, wherein

[0016] the pre-set number of terminals being constructed so as not beingelectrically connected to one another by the heat radiating paths andthe heat sink members.

[0017] In the semiconductor device, in at least one of the heatdissipating paths, there is inserted in a path reaching the heat sinkmember a member exhibiting good thermal conductivity and electricallyinsulating properties, termed as an “insulating member”.

[0018] Also there is provided a semiconductor device wherein a firstterminal of the active element is connected via an electricallyconductive member to a heat sink member, and wherein a second terminalof the active element transmits heat to the heat sink member via atleast an insulating member interposed in-between.

[0019] In one aspect, the present invention provides an arrangement inwhich an electrically conductive member connected to a terminal of anactive element formed on a substrate is connected via an insulatingmember to the other terminal of said active element and in which saidelectrically conductive member is connected to a heat sink member of thepackage accommodating said active element.

[0020] In another aspect, the present invention provides an arrangementin which a terminal of an active element formed on a substrate isconnected via an insulating member to a heat sink member of a packageused for mounting said active element.

[0021] The present invention provides a method for producing asemiconductor device in which an active element formed on a substrate isconnected to a heat sink member of a package accommodating the activeelement, comprising the steps of:

[0022] (a) forming a gate electrode on the substrate;

[0023] (b) forming a first insulating film having holes provided in thesubstrate at positions of a drain electrode and a source electroderespectively;

[0024] (c) forming the drain electrode and the source electrode on thesubstrate;

[0025] (d) forming a second insulating film on the entire surface of thesubstrate and planarizing the surface until the drain electrode and thesource electrode are exposed;

[0026] (e) forming an insulating member on the drain electrode;

[0027] (f) forming on the substrate a third insulating film having ahole provided in register with the source electrode and planarizing thesurface until the surface of the insulating member of the drainelectrode is exposed; and

[0028] (g) forming an electrically conductive member on the thirdinsulating film.

[0029] Preferably, all or part of the insulating member may be a membercomprising aluminum nitride, while a high-output-power FET formed on aGaAs substrate may be used as an active element.

[0030] Other features of the present invention will become apparent fromthe entire disclosure including claims and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is a cross-sectional view showing a semiconductor deviceaccording to a first embodiment of the present invention.

[0032]FIG. 2 is a cross-sectional view showing, step-by-step, themanufacturing method for the semiconductor device according to a firstembodiment of the present invention.

[0033]FIG. 3 is a cross-sectional view showing, step-by-step, themanufacturing method for the semiconductor device according to a firstembodiment of the present invention.

[0034]FIG. 4 is a cross-sectional view showing, step-by-step, themanufacturing method for the semiconductor device according to a firstembodiment of the present invention.

[0035]FIG. 5 is a cross-sectional view showing, step-by-step, themanufacturing method for the semiconductor device according to a firstembodiment of the present invention.

[0036]FIG. 6 is a cross-sectional view showing the mounted state of thesemiconductor device according to the first embodiment of the presentinvention.

[0037]FIG. 7 is a schematic cross-sectional view showing the state ofthermal diffusion (heat dissipation) of the semiconductor deviceaccording to the first embodiment of the present invention.

[0038]FIG. 8 is a cross-sectional view showing a semiconductor deviceaccording to a second embodiment of the present invention.

[0039]FIG. 9 is a cross-sectional view showing the mounted state of thesemiconductor device according to the second embodiment of the presentinvention.

[0040]FIG. 10 is a cross-sectional view showing a semiconductor deviceaccording to a third embodiment of the present invention.

[0041]FIG. 11 is a cross-sectional view showing the mounted state of thesemiconductor device according to the third embodiment of the presentinvention.

[0042]FIG. 12 illustrates a conventional semiconductor device.

[0043]FIG. 13 is a cross-sectional view showing the mounted state of theconventional semiconductor device.

[0044]FIG. 14 is a schematic cross-sectional view showing the state ofthermal diffusion (heat dissipation) of the semiconductor device.

PREFERRED EMBODIMENTS OF THE INVENTION

[0045] The present invention is hereinafter explained in detail withreference to a preferred embodiment and examples of execution showingthe manner of executing the embodiment.

[0046] In a preferred embodiment of the fine wiring/interconnectionforming method of the present invention, an insulator of high electricalinsulating properties and good thermal conductivity (such as aluminumnitride (5 of FIG. 6)) is formed on one of electrodes (such as drainelectrode (3 of FIG. 6)) of an active element formed on a semiconductorsubstrate of a semiconductor device. The active element is connected toa package. The insulator is connected to an interconnection layer of theother electrode (such as an interconnection layer of a source electrode(6 of FIG. 6) or to a heat sink of the package (9 of FIG. 9).

[0047] Alternatively, an insulator of high electrical insulatingproperties and good thermal conductivity (such as aluminum nitride (5 ofFIG. 6)) is formed on a heat sink (9 of FIG. 9) and is contacted with anelectrode of the active element, such as a drain electrode (3 of FIG.6).

EXAMPLES

[0048] For illustrating the embodiments of the present invention infurther detail, reference is had to the drawings by way of illustratingexamples of the present invention.

Example 1

[0049] A first example of execution of the present invention ishereinafter explained. FIGS. 1 to 5 are cross-sectional views forillustrating the first example of the manufacturing method for thesemiconductor device according to the present invention, wherein FIG. 1shows the cross-section of the active element and FIGS. 2 to 5 arecross-sectional views showing the manufacturing method thereofstep-by-step. FIG. 6 is a cross-sectional view schematically showing thestate of mounting the active element on the package and FIG. 7 is across-sectional view schematically showing the state of thermaldiffusion (heat dissipation) to the package.

[0050] First, a gate electrode 2 is formed on a substrate 1 of GaAs etcusing a known technique and a first insulating film 7 is then depositedon the entire surface of the substrate 1.

[0051] In the portions of the first insulating film 7 where to form asource electrode 4 and a drain electrode 3 are formed openings and metalsuch as TiAu operating as a electrically conductive layer for plating isformed by sputtering to cause growth of metals such as Au to form thesource electrode 4 and the drain electrode 3.

[0052] Then, a second insulating film 8 is deposited to overlie thefirst insulating film 7, source electrode 4 and the drain electrode 3.The resulting assembly is planarized using a known technique and etchedback until the drain electrode 3 and the source electrode 4 are exposedto outside. (refer to FIG. 3)

[0053] An insulating member having high electrical insulating propertiesand thermal conductivity, such as aluminum nitride 5, is deposited onthe entire surface of the substrate 1, using a chemical gas phasedeposition (CVD). After coating a photoresist on the insulating member,the resist 10 is left only on the portion of the substrate surface inregister with the drain electrode 3, by a known lithographic technique,and aluminum nitride on the exposed portion is etched off.

[0054] Referring to FIG. 4, an insulating film 12 is deposited on theentire surface of the substrate 1, and subsequently the insulating film12 is etched back for planarization, until aluminum nitride 5 isexposed. A portion of the insulating film 12 in register with the sourceelectrode 4 is etched off to form an opening.

[0055] Then, a film of a metal, such as TiAu, operating as anelectrically conductive layer for plating, is formed by a sputteringmethod etc. The metal such as Au is then grown by, for example, plating,to form an electrically conductive member (layer) 6. Since aluminumnitride 5 is exposed in this state in order to form the the electricallyconductive members 6 for plating TiAu and Au, the electricallyconductive member 6 is also formed on the aluminum nitride 5 to assuresufficient thermal contact.

[0056] Finally, a heat sink of the active element and a packagemanufactured by the above process is mounted in accordance with theface-down system as shown in FIG. 6.

[0057] The above-described first embodiment of the present invention hasthe following meritorious effects. FIG. 7 schematically shows the effectof the first embodiment of the present invention. Referring to FIG. 7,heat evolved from an active element is radiated not only from the sourceelectrode 4 but also from the drain electrode 3 via the electricallyconductive member 6 and the aluminum nitride 5 exhibiting high thermalconductivity. Thus, the heat evolved from the active element is radiatedvia two channels to improve the thermal dissipation efficiency higherthan that is possible with the conventional device.

Example 2

[0058] Next, a second example of the present invention is explained withreference to FIGS. 8 and 9 showing semiconductor device according to thepresent invention. Reference is had to FIGS. 2 and 3 explained withreference to the first Example as to the manufacturing method of thesecond Example of the present invention. The second Example, nowexplained, differs from the first Example mainly in that a protrusion ofmetal formed by Au plating is provided on a portion in register with thesource electrode on the heat sink side of the package. First, themanufacturing method of the present example is explained.

[0059] On the substrate 1, a gate electrode 2, a first insulating film7, a drain electrode 3 and a source electrode 4 are formed, using aconventional technique (see FIG. 2).

[0060] Then, a second insulating film 8 is deposited on the entiresurface of the GaAs substrate 1, and the resulting assembly is etchedback until the drain electrode 3 and the source electrode 4 are exposed.

[0061] Then, using the CVD method etc, aluminum nitride 5 is depositedon the entire surface of the substrate 1. After coating a photoresist onthe insulator 5, the resist 10 is left only on a portion of thesubstrate 1 in register with the drain electrode 3, and aluminum nitride5 of the exposed portion is etched off, with a use of a knownphotolithographic technique.

[0062] In the present Example, Au plating 11 is applied to a portion ofthe heat sink 9 of the flip-chip mounted package which faces the sourceelectrode 4 of the active element bonded to the heat sink 9, as shown inFIG. 8.

[0063] The active element and the package, prepared as described above,are positioned so that the source electrode 4 of the active elementfaces/abuts to the Au plating 11 on the heat sink 9 of the package, andthe active element and the package are bonded to each other by thermalpressure bonding for mounting, as shown in FIG. 9.

[0064] In the present Example, similarly to the first Example, heatgenerated by the active element is radiated to the heat sink 9 of thepackage not only from the source electrode 4 but also from the drainelectrode 3 via the aluminum nitride 5 of high thermal conductivity.Moreover, since aluminum nitride 5 is directly contacted with the heatsink of the package, heat radiation efficiency is improved further.

Third Example

[0065] Next, a third example of the present invention is explained withreference to FIGS. 10 and 11 showing a semiconductor device and amanufacturing method thereof according to the third example of thepresent invention. Reference is had to FIG. 2 explained with referenceto the first Example as to the manufacturing method of the third Exampleof the present invention. The second Example, now explained, differsfrom the first Example mainly in that a protrusion of metal formed by Auplating is provided on a portion in register with the source electrodeon the heat sink side of the package and in that aluminum nitride isprovided on a portion of the heat sink side in register with the drainelectrode 3. First, the manufacturing method of the present invention isexplained.

[0066] In the present Example, similarly to the first Example, describedabove, a gate electrode 2, a first insulating film 7, a drain electrode3 and a source electrode 4 are formed by known techniques (FIG. 2).

[0067] In the present Example, Au plating 11 is applied to a portion ofthe heat sink 9 of the flip-chip mounted package which faces the sourceelectrode 4 of the active element when the heat sink 9 is bonded to thesource electrode 4, while aluminum nitride 5 is deposited on the portionof the heat sink 9 facing the drain electrode 3, as shown in FIG. 10.

[0068] The active element and the package, prepared as described above,are positioned so that the source electrode 4 of the active elementfaces the Au plating 11 on the heat sink 9 of the package, and so thatthe drain electrode 3 faces the aluminum nitride 5. In this state, theactive element and the package are bonded to each other by thermalpressure bonding for mounting, as shown in FIG. 9.

[0069] In the present Example, similarly to the first Example, heatgenerated by the active element is radiated to the heat sink 9 of thepackage, via the aluminum nitride 5 of high thermal conductivity, notonly from the source electrode 4 but also from the drain electrode 3. Inthe present Example, there is no necessity of forming the secondinsulating film, planarizing the insulating film or provision of hole onthe side of the active element, thus significantly reducing the numberof production steps.

[0070] Although aluminum nitride 5 is used in the above Example as aninsulating member having superior thermal conductivity, it is sufficientif a material exhibits equivalent or superior properties, and forinstance, alumina may be used.

[0071] It is unnecessary for the entire insulating member to exhibitinsulating properties, it being only sufficient if an insulator issufficient to assure electrical insulation of the heat sink member and aterminal of the active element connected to the insulating member isprovided at a portion of a member designated herein as the insulatingmember.

[0072] The meritorious effect of the invention of the present inventionare summarised as follows.

[0073] As explained in the foregoing, the present invention has thefollowing meritorious effects.

[0074] The first meritorious effect of the present invention is that theheat evolved by the active element is radiated to the heat sink of thepackage via the electrically conductive member and a materisl (e.g.aluminum nitride) of high thermal conductivity not only from the sourceelectrode but also from the drain electrode, so that the heat evolved bythe active element is radiated via two or more paths, thus improving theheat diffusion/dissipation efficiency as compared to the conventionalsystem.

[0075] The second meritorious effect of the present invention is thatthe number of the production steps for producing the semiconductordevice can be reduced by providing the gold plating area or the area ofinsulating material (aluminum nitride) on the package side.

[0076] It should be noted that other objects of the present inventionwill become apparent in the entire disclosure and that modifications maybe done without departing the gist and scope of the present invention asdisclosed herein and appended herewith.

[0077] Also it should be noted that any combination of the disclosedand/or claimed elements, matters and/or items may fall under themodifications aforementioned.

What is claimed is:
 1. A semiconductor device comprising: a plurality ofheat dissipating paths, each for each of a pre-set number of terminalsof an active element, said heat dissipating paths being adapted fortransmitting heat from the terminals of said active element to a heatsink member, wherein said pre-set number of terminals being constructedso as not being electrically connected to one another by said heatradiating paths and said heat sink members.
 2. The semiconductor deviceas defined in claim 1 wherein, in at least one of the heat dissipatingpaths, there is inserted in a path reaching said heat sink member amember exhibiting good thermal conductivity and electrically insulatingproperties,termed as an “insulating member”.
 3. A semiconductor devicewherein a first terminal of the active element is connected via anelectrically conductive member to a heat sink member, and wherein asecond terminal of the active element transmits heat to said heat sinkmember via at least an insulating member interposed in-between.
 4. Thesemiconductor device as defined in claim 1 wherein said heat sink memberis a heat sink member of a package mounting the active element.
 5. Thesemiconductor device as defined in claim 2 wherein said heat sink memberis a heat sink member of a package mounting the active element.
 6. Thesemiconductor device as defined in claim 3 wherein said heat sink memberis a heat sink member of a package mounting the active element.
 7. Asemiconductor device wherein an electrode of an active element formed ona substrate, termed as a “first electrode”, is connected to anelectrically conductive member, and at least one of the other electrodesof the active element, termed as a “second electrode”, is connected tosaid electrically conductive member via an insulating member, saidelectrically conductive member abutting to a heat sink member of apackage.
 8. The semiconductor device as defined in claim 7 wherein saidactive element is comprised of a field effect transistor FET, andwherein said first and second electrodes are a source electrode and adrain electrode, respectively.
 9. A semiconductor device wherein atleast one terminal of an active element is connected via an insulatingmember to a heat sink member of a package used for mounting the activeelement.
 10. The semiconductor device as defined in claim 9 wherein saidinsulating member is arranged on at least one of (a) a terminal surfaceof said active element and/or (b) a heat sink member side of the packageused for mounting the active element.
 11. The semiconductor device asdefined in claim 2 wherein the insulating member comprises aluminumnitride.
 12. A method for producing a semiconductor device in which anactive element formed on a substrate is connected to a heat sink memberof a package accommodating said active element, comprising the steps of:(a) forming a gate electrode on said substrate; (b) forming a firstinsulating film having holes provided in the substrate at position of adrain electrode and a source electrode respectively; (c) forming saiddrain electrode and said source electrode on said substrate; (d) forminga second insulating film on the entire surface of said substrate andplanarizing the surface until said drain electrode and the sourceelectrode are exposed; (e) forming an insulating member on said drainelectrode; (f) forming on said substrate a third insulating film havinga hole provided at the position of the source electrode and planarizingthe surface until the surface of said insulating member of said drainelectrode is exposed; and (g) forming an electrically conductive memberon said third insulating film.
 13. A method for producing asemiconductor device in which an active element formed on a substrate isconnected to a heat sink member of a package accommodating said activeelement, comprising the steps of: (a) forming a gate electrode on saidsubstrate; (b) forming a first insulating film having holes provided inthe substrate at positions of a drain electrode and a source electrode,respectively; (c) forming said drain electrode and the source electrodeon said substrate; (d) forming a second insulating film on the entiresurface of the substrate and planarizing the surface until the drainelectrode and the source electrode are exposed; (e) forming aninsulating member on said drain electrode; (f) forming a metalprotuberance on said package in register with the source electrode ofsaid active element; and (g) bonding said active element and the packageso that said source electrode of said active element and the metalprotuberance of the package face each other.
 14. A method for producinga semiconductor device in which an active element formed on a substrateis connected to a heat sink member of a package accommodating saidactive element, comprising the steps of: (a) forming a gate electrode onsaid substrate; (b) forming a first insulating film having holesprovided in the substrate at positions of a drain electrode and a sourceelectrode respectively; (c) forming said drain electrode and said sourceelectrode on said substrate; (d) providing on said package an insulatingmember at a position facing the drain electrode of said active element;(e) providing a metal protuberance on said package in register with thesource electrode of said active element; (f) bonding said active elementand the package so that said source electrode of said active element andthe metal protuberance of said package face each other and so that thedrain electrode and the insulating member of said package face eachother.
 15. The method for producing a semiconductor device as defined inclaim 12 wherein said insulating member comprises aluminum nitride. 16.The method for producing a semiconductor device as defined in claim 13wherein said insulating member comprises aluminum nitride.
 17. Themethod for producing a semiconductor device as defined in claim 14wherein said insulating member comprises aluminum nitride.
 18. Themethod for producing a semiconductor device as defined in claim 12wherein said active element is a high-output-power FET formed on a GaAssubstrate and wherein said insulating member comprises aluminum nitride.19. The method for producing a semiconductor device as defined in claim13 wherein said active element is a high-output-power FET formed on aGaAs substrate and wherein said insulating member comprises aluminumnitride.
 20. The method for producing a semiconductor device as definedin claim 14 wherein said active element is a high-output-power FETformed on a GaAs substrate and wherein said insulating member comprisesaluminum nitride.